My friends look at me like I have 3 heads when they see my engine bay as you could literally eat off it most days but only if you were wearing sunglasses.
I honestly don't know a single friend or family member who cleans their engine bay except me. A few keep the exterior and interior spotless while others have never cleaned/vacuumed the interior or washed/waxed their vehicles.
I have one friend who is meticulous with maintenance on all his vehicles but aside from one single yearly drive through carwash never cleans his vehicles until the day before he puts them up for sale or trades in.
And he still gets top dollar, for all of them. I actually have to move stuff on the seat and floor just to set in his 4-Runner when I get in it.
I used to wash his motorcycles before we went riding as I too embarrassed to be seen with him on his BMW touring bike with so much dirt, pine sap & needles on it you couldn't tell what it was.
I went to get inspected for him once and the brake light didn't work when I popped the seat off mice ran everywhere, scared the crap out the inspection guy.
I removed the mouse nest and fixed the loose wire.

As for the fuel pump rust area I would still clean it with a liquid rust remover and then put some clear coat on it.
If they are worried about warranty, I'd ask Mazda if that would void the warranty or not and get it in writing.

 

I can tell you that this would never come form Mazda Corp, and if a dealership did write it MAZDA corp would not in anyway be obligated to warranty the part. Dealerships can't change Mazda warranty policies.

I think my picking at the OP and how dirty engine compartment is more or less to make a point for other reading that like you pointed out it not an imposable task to clean the engine compartment once in a while if anything else a few minutes spray with the garden hose and leave the hood open a few hours.

BTW if you blow up the pictures there is some more evidence that mighty suggest something else went on....

I still would like an explanation of what that dust is all over the engine compartment. I have a theory..

 

No recent volcanoes, looks like forest fire smoke to me, which has many corrosive materials that will do that.
In my area we had a cement plant, which before EPA regulations, would send out lime dust up to 7 miles away depending on the wind.
That stuff if not washed off almost immediately would eat through paint and chrome.
It was so bad some of the local car dealers withing a mile, had to wash the cars every week and occasionally daily when wind direction changed.